This invention relates to thread monitors for textile machines, and more particularly to thread monitors for stopping operation of a sewing machine upon breakage of the thread supplied to the needle of the sewing machine. Previously known thread monitors of the type shown in German Auslegeschrift No. 1,226,013 and U.S. Pat. Nos. 2,251,368 and 3,922,981 have a thread feeler supported in an unstable equilibrium (i.e., against a gravity bias) by the thread supplied to the needle of a sewing machine. Upon thread breakage, the feeler drops into its stable equilibrium by its own weight and in this position operates a switch-off mechanism or control means for stopping the operation of the machine.
Other previously known thread monitors of the type shown in German Gebrauchsmuster No. 1,914,424 and U.S. Pat. No. 3,714,916 have a feeler biased into engagement with the thread by a spring or magnetic device. When the machine is in operation, the feeler is kept in a sensing or retracted position by the pull exerted by the thread. When a thread break occurs, the spring or magnetic bias moves the feeler to its operative position for operating the switch-off mechanism or control means.
The disadvantage of these previously known monitors is that when the machine is stopped for reasons other than thread breakage or running out of thread the pull on the thread is relieved and the biased feeler moves to the position for operating the switch-off mechanism the same as if there had been a thread breakage. Thus, in order to resume operation of the machine, the feeler must be moved away from this position, or the control circuit for the drive means to the machine must be designed such that the interruption caused by the feeler will be cancelled when the machine is switched on again.
Another disadvantage is that the end of the thread at the needle remaining after thread trimming is pulled out of the needle eye by the feeler as it moves when the machine is stopped. To prevent this, the end of the thread has in the past been trapped by a thread nipper.